Wireless monitoring of laboratory animals

Abstract

Systems and methods for monitoring laboratory animals includes a tag comprising an inductive element and a capacitive element attached to a portion of a laboratory animal. The position of the portion is detected by monitoring the effect of the tag on a time-varying magnetic field having different frequencies, one near tag resonance, and one away from tag resonance.

What is claimed is: 
     
       1. A system for detecting the position of a portion of a laboratory animal, comprising:
 a first coil and a second coil aligned along a longitudinal axis, wherein a laboratory animal is placed on a floor located at approximately the mid point between the first and second coil; 
 a resonant circuit attached to a portion of said laboratory animal, said resonant circuit defining a resonant frequency; 
 a signal generator electrically coupled to said coil and configured to drive said at least one coil with at least a first drive signal comprising a first frequency and a second drive signal comprising a second frequency, wherein the second frequency is more distant from said resonant frequency than the first frequency; and 
 a detection circuit coupled to said at least one coil and configured to detect an impedance change in said at least one coil between application of said first frequency to said at least one coil and application of said second frequency to said at least one coil, and to generate an output signal representative of resonant circuit position with respect to said at least one coil based at least in part on said impedance change. 
 
     
     
       2. The system of  claim 1 , wherein said detection circuit generates at least a first measurement signal when the first drive signal comprises said first frequency and a second measurement signal when the second drive signal comprises said second frequency, the first measurement signal and the second measurement signal having a difference therebetween, and wherein the difference between the first and second measurement signals is representative of resonant circuit position with respect to said at least one coil. 
     
     
       3. The system of  claim 1 , wherein said two coils are connected as two legs of a bridge circuit. 
     
     
       4. The system of  claim 3 , wherein the signal generator is coupled to opposite nodes of said bridge. 
     
     
       5. The system of  claim 4 , wherein the detection circuit is coupled to opposite nodes of said bridge. 
     
     
       6. The system of  claim 1 , wherein said resonant circuit comprises an inductor and a capacitor electrically coupled in parallel. 
     
     
       7. The system of  claim 1 , wherein within the signal generator is configured to sweep the frequency of the drive signal through a frequency range including the resonant frequency of the resonant circuit. 
     
     
       8. The system of  claim 1 , wherein the output signal is representative of the vertical position of said resonant circuit with respect to said floor. 
     
     
       9. The system of  claim 8 , wherein the output signal is substantially independent of the horizontal position of said tag with respect to said floor. 
     
     
       10. The system of  claim 1 , wherein the first and second coils are wired in series, the system comprises a bridge of four legs, wherein the first and second coils form two legs of a bridge. 
     
     
       11. The system of  claim 1 , wherein said resonant circuit is mounted to a printed circuit board. 
     
     
       12. The system of  claim 1 , wherein said portion of said laboratory animal comprises a paw of a rodent. 
     
     
       13. The system of  claim 1 , wherein said portion of said laboratory animal comprises a head of a rodent. 
     
     
       14. A method of detecting the position of a portion of a laboratory animal, comprising:
 attaching a resonant circuit to said portion of said laboratory animal; 
 placing said laboratory animal on a floor located at approximately a midpoint between a first coil and a second coil aligned along a longitudinal axis separated by a vertical distance; 
 driving said at least one coil with a signal of at least a first frequency and a second frequency; and 
 detecting an impedance change in said at least one coil between said first and second frequencies. 
 
     
     
       15. The method of  claim 14 , comprising generating a first measurement signal at said first frequency and a second measurement signal at said second frequency, and determining a difference between said first measurement signal and said second measurement signal. 
     
     
       16. The method of  claim 15 , wherein the difference between the first and second measurement signals is related to a vertical distance between said resonant circuit and said floor. 
     
     
       17. The method of  claim 14 , wherein the second frequency is more distant from the resonant frequency of the resonant circuit than the first frequency. 
     
     
       18. A method of assaying for an anti-nociceptive drug, comprising:
 attaching a resonant circuit to a paw of a rodent; 
 administering a potential anti-nociceptive drug to a rodent; 
 exposing said paw to a nociceptive stimulus; 
 placing said rodent on a floor located at approximately a midpoint between a first coil and a second coil aligned along a longitudinal axis, the first and second coils separated by a vertical distance; 
 driving said at least one coil with a signal of at least a first frequency and a second frequency; and 
 detecting paw guarding by detecting an impedance change in the first coil and the second coil between said first and second frequencies. 
 
     
     
       19. The method of  claim 18 , comprising generating a first measurement signal at said first frequency and a second measurement signal at said second frequency, and determining a difference between said first measurement signal and said second measurement signal. 
     
     
       20. The method of  claim 19 , wherein the difference between the first and second measurement signals is related to the vertical distance between said resonant circuit and said floor. 
     
     
       21. The method of  claim 18 , wherein the second frequency is more distant from the resonant frequency of the resonant circuit than the first frequency.